Thermal ink ject defect tolerant resistor design

ABSTRACT

Thermal ink jet defect tolerant resistor designs are described. In one embodiment, a thermal ink jet resistor structure comprises a first resistor element and at least one other resistor element. The resistor elements are connected in parallel and have substantially the same resistances. The resistor elements are configured for redundancy such that if one of the resistor elements fails, one or more remaining resistor elements can function to effectuate ink ejection. In another embodiment, a thermal ink jet printer comprises multiple ink reservoirs configured for holding and ejecting ink toward a print medium. At least one resistor array is disposed within each ink reservoir. Each resistor array comprises multiple, redundant resistor elements that are connected in parallel with one another such that failure of any one resistor element will not render its associated ink reservoir inoperative. A source of voltage pulses is operably associated with said at least one resistor array and is configured to supply voltage pulses thereto for heating the resistor arrays effective to nucleate the ink within an associated ink reservoir.

TECHNICAL FIELD

[0001] The present invention relates to print heads for thermal ink jetprinters and, more particularly, to print head systems and methods ofoperating thermal ink jet printers.

BACKGROUND

[0002] In the field of thermal ink jet printing, it has become a commonpractice to provide heater resistors on a common substrate and alignthese heater resistors with individual ink reservoirs and correspondingink ejection orifices in an outer nozzle plate. These heater resistorsare physically defined and electrically driven by conductive traceswhich can be photolithographically formed on the surface of a suitableresistor layer material, such as tantalum-aluminum. These heaterresistors have been traditionally isolated from the overlying inkreservoirs by dielectric materials such as silicon carbide and siliconnitride. This type of thermal ink jet printhead is described, forexample, in the Hewlett Packard Journal, Vol. 36, No. 5, May 1985,incorporated herein by reference.

[0003] Consider, for example, FIG. 1 which shows a cross-sectional viewof an exemplary ink reservoir and resistor for ejecting ink.Specifically, a substrate 102 such as silicon, supports a number of inkreservoirs 104. Each reservoir is configured to receive ink that is tobe ejected. A heater or resistor 106 is disposed within the reservoir,and a passavation layer 107 comprising a dielectric material is formedover the resistor 106. To expel a jet of ink, the heater or resistor isheated rapidly which causes a vapor bubble 108 to form within the inkreservoir 104. This vapor bubble then causes a quantity of ink 110 to beejected out of the channel and towards a page that is to be printedupon.

[0004] One of the problems associated with ink jet printers and,particularly, the resistors that are used as heaters to heat the ink, isthat over time, the resistor can begin to work improperly due to defectsthat are present in the material of the resistor. Improper resistoroperation can also be caused by things such as contamination or voids inlayers that are either over or under the resistor, and the presence ofvoids or cavitation damage. Specifically, resistors are typically formedusing thin film techniques where a conductive material, such as tantalumaluminum, is deposited over a substrate and etched to form a desiredresistor. This layer is a very thin layer. The resistor layer can havematerial defects in it which, over time and due in large part to thecontinual heating and cooling of the material, cause the resistor toeffectively malfunction, open up or fuse. When the resistor fails towork, ink cannot be ejected from the ink reservoir and, hence, theintegrity of the printer in which the resistor resides can becompromised.

SUMMARY

[0005] Thermal ink jet defect tolerant resistor designs are described.In one embodiment, a thermal ink jet resistor structure comprises afirst resistor element and at least one other resistor element. Theresistor elements are connected in parallel and have substantially thesame resistances. The resistor elements are configured for redundancysuch that if one of the resistor elements fails, one or more remainingresistor elements can function to effectuate ink ejection.

[0006] In another embodiment, a thermal ink jet printer comprisesmultiple ink reservoirs configured for holding and ejecting ink toward aprint medium. At least one resistor array is disposed within each inkreservoir. Each resistor array comprises multiple, redundant resistorelements that are connected in parallel with one another such thatfailure of any one resistor element will not render its associated inkreservoir inoperative. A source of voltage pulses is operably associatedwith the one resistor array and is configured to supply voltage pulsesthereto for heating the resistor arrays effective to nucleate the inkwithin an associated ink reservoir. In one aspect, a resistance sensoris provided and is coupled with the source of voltage pulses. Theresistance sensor is configured to sense a change in resistance of theone resistor array. The source of voltage pulses is responsive to aresistance change to modify the voltage pulses that are supplied to theone resistor array.

[0007] A method of forming a thermal ink jet resistor structure for usein nucleating ink comprises forming a layer of conductive material overa substrate. The layer of conductive material is patterned and etchedeffective to form multiple, parallel-connected resistor elements. Theresistor elements are configured such that failure of any one resistorelement will not render the resistor structure inoperative fornucleating ink.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a cross-sectional view of an exemplary ink jet reservoiremploying resistors for nucleating an amount of ink for ejection.

[0009]FIG. 2 is a cross-sectional view of a substrate fragment inprocess in accordance with one embodiment.

[0010]FIG. 3 is a cross-sectional view of the FIG. 2 substrate fragmentin process in accordance with one embodiment.

[0011]FIG. 4 is a cross-sectional view of the FIG. 3 substrate fragmentin process in accordance with one embodiment.

[0012]FIG. 5 is a cross-sectional view of the FIG. 4 substrate fragmentin process in accordance with one embodiment.

[0013]FIG. 6 is a cross-sectional view of the FIG. 5 substrate fragmentin process in accordance with one embodiment.

[0014]FIG. 7 is a top plan view of the FIG. 6 substrate fragment.

[0015]FIG. 8 is a schematic view of an exemplary resistor arraycomprising multiple redundant resistor elements in accordance with onedescribed embodiment.

DETAILED DESCRIPTION

[0016] Overview

[0017] In accordance with the described embodiments, redundant ink jetresistor arrays are provided. Each ink reservoir that contains ink forinjection is provided with one resistor array to nucleate the ink orprovide the vapor bubble. Each resistor array comprises multipleresistors that are connected in parallel. The parallel resistors havesubstantially the same resistance. The resistor array is the onlyresistive structure that is utilized for ejecting ink. To eject ink,voltage pulses of a prescribed magnitude are applied to the resistorarray to effectively heat the ink to form the vapor bubble. The resistorarrays preclude redistribution of current caused by a local defect,particle or void as would happen in the case of a single resistor. Inthe event that one of the resistors of the array fails, the otherparallel resistors can continue to operate to eject ink.

[0018] For additional background information in ink jet printers, thereader is referred to U.S. Pat. Nos. 5,016,023, 5,610,644, 5,870,125,4,695,853, and 5,491,502, the disclosures of which are incorporated byreference herein. An exemplary ink jet printer in which the variousembodiments can be implemented is shown in FIG. 9 at 900.

[0019] Exemplary Embodiment

[0020] Referring to FIG. 2, a substrate fragment is shown at 112 andcomprises the substrate upon which the resistor arrays are to be formed.Substrate 112 can comprise any suitable material. In the illustrated anddescribed embodiment, the substrate can comprise glass, SiO₂, SiO₂ overSi, or SiO₂ over glass. A conductive layer 114 is formed over substrate112 and comprises material from which the resistor arrays are to beformed. Any suitable conductive material can be used. In the illustratedand described embodiment, layer 114 comprises a tantalum aluminummaterial that is typically used to form ink jet heater/resistorelements. Other suitable conductive materials include, withoutlimitation, refractory materials such as refractory material alloys. Inthe discussion that follows, the resistor array formation process isdescribed with respect to one resistor array comprising multipleresistors. It is to be understood that elsewhere on the substrate otherresistor arrays are contemporaneously formed.

[0021] Referring to FIG. 3, a masking layer 116 is formed overconductive layer 114. Any suitable masking layer material can be used.An exemplary material comprises photoresist.

[0022] Referring to FIG. 4, masking layer 116 is exposed and patternedto form a resistor array pattern generally indicated at 118. Standardknown techniques can be utilized to expose and pattern masking layer116.

[0023] Referring to FIGS. 5 and 6, conductive layer 114 is etched toform a plurality of resistor elements 120. Collectively, the resistorselements are connected in parallel and form one resistor array 122.Advantageously, each of the resistor elements has substantially the sameresistance. Any suitable number of resistor elements can be provided. Inthe illustrated and described embodiment, ten such resistors are shown.Each resistor array comprises the only resistive structure orheater/resistor structure that is utilized to eject ink.

[0024] Referring to FIG. 7, a top plan view of resistor array 122 isshown. The individual resistors of the array are isolated from oneanother except at conductor junctions that are not specificallyillustrated.

[0025]FIG. 8 is an electrical schematic diagram of one exemplaryresistor array configured for use in connection with an ink reservoir toeject ink. To eject ink, a series of voltage pulses are generated by apulse generator 124 and applied to the resistor array. In the event thatone or more of the resistors fails, the other parallel-connectedresistors can still function to nucleate the ink thus causing it toeject. In an alternate embodiment, the voltage pulse generator caninclude a resistance sensor 125. The purpose of the resistance sensor125 is to sense the resistance of the multiple parallel resistors. Inthe event that one or more of the resistors fails, the overallresistance of the parallel array of resistors changes. Upon sensing achange in the overall resistance of the resistors, the voltage pulsegenerator can then modify the power input or voltage pulses that is(are) delivered to the resistor array.

[0026] The present embodiments constitute improvements over past ink jetresistor constructions in that now, a redundant array of multipleresistors is provided. The failure of one or more of the individualresistor elements will not necessarily mean failure of the individualejector structure of which the array comprises a part. Further, use ofthe described voltage pulses in connection with the multiple parallelresistors will ensure that any remaining resistor elements (after lossof one or more elements), will not be excessively over-stressed.

[0027] The inventor is aware of one particular resistor constructionthat uses a pair of so-called converters for converting electricalenergy to heat energy, and a so-called distributor to distribute ordissipate the heat energy created by the converters. Such is describedin U.S. Pat. No. 5,933,166. The presently-described embodiments aredifferent from this construction and provide advantages that are notembodied in the construction. For example, in the present example, allof the multiple resistor elements are essentially the same inconstruction, material, resistivity and the like. This similarityenhances the resistor array's advantageous redundant characteristics.The construction described in the '166 patent does not have resistorsthat are redundant. In addition, failure of one of the converters or thedistributor will render the system useless for ejecting ink.

[0028] Although the invention has been described in language specific tostructural features and/or methodological steps, it is to be understoodthat the invention defined in the appended claims is not necessarilylimited to the specific features or steps described. Rather, thespecific features and steps are disclosed as preferred forms ofimplementing the claimed invention.

1. A thermal ink jet resistor structure comprising: a first resistorelement; and at least one other resistor element, the resistor elementsbeing connected in parallel and having substantially the sameresistances, the resistor elements being configured for redundancy suchthat if one of the resistor elements fails, one or more remainingresistor elements can function to effectuate ink ejection.
 2. Thethermal ink jet resistor structure of claim 1, wherein the resistorelements comprise the same material.
 3. The thermal ink jet resistorstructure of claim 1, wherein the resistor elements comprise a resistorarray that is the only resistive structure that is utilized for ejectingink.
 4. The thermal ink jet resistor structure of claim 1, wherein theresistor elements comprise tantalum aluminum.
 5. The thermal ink jetresistor structure of claim 1, wherein the resistor elements comprise arefractory material.
 6. The thermal ink jet resistor structure of claim1, wherein the resistor elements comprise a resistor array that is theonly resistive structure that is utilized for ejecting ink, and whereinthe resistor elements comprise the same material.
 7. The thermal ink jetresistor structure of claim 1, wherein the resistor elements comprise aresistor array that is the only resistive structure that is utilized forejecting ink, and wherein the resistor elements comprise tantalumaluminum.
 8. A thermal ink jet printer comprising: multiple inkreservoirs configured for holding and ejecting ink toward a printmedium; at least one resistor array disposed within each ink reservoir,each resistor array comprising multiple, redundant resistor elementsconnected in parallel with one another such that failure of any oneresistor element will not render its associated ink reservoirinoperative; and a source of voltage pulses operably associated withsaid at least one resistor array and configured to supply voltage pulsesthereto for heating the resistor arrays effective to nucleate the inkwithin an associated ink reservoir.
 9. The thermal ink jet printer ofclaim 8 further comprising a resistance sensor coupled with the sourceof voltage pulses and configured to sense a change in resistance of theat least one resistor array, the source of voltage pulses beingresponsive to a resistance change to modify the voltage pulses that aresupplied to the at least one resistor array.
 10. The thermal ink jetprinter of claim 8, wherein each of the resistor elements comprises thesame material, each resistor array being the only resistive structurethat nucleates the ink.
 11. The thermal ink jet printer of claim 8,wherein each of the resistor elements has substantially the sameresistance, each resistor array being the only resistive structure thatnucleates the ink.
 12. The thermal ink jet printer of claim 8, whereineach of the resistor elements comprises the same material and hassubstantially the same resistance, each resistor array being the onlyresistive structure that nucleates the ink.
 13. The thermal ink jetprinter of claim 8, wherein each of the resistor elements comprisestantalum aluminum, and has substantially the same resistance, eachresistor array being the only resistive structure that nucleates theink.
 14. A method of forming a thermal ink jet resistor structure foruse in nucleating ink, the method comprising: forming a layer ofconductive material over a substrate; and patterning and etching thelayer of conductive material effective to form multiple,parallel-connected resistor elements, the resistor elements beingconfigured such that failure of any one resistor element will not renderthe resistor structure inoperative for nucleating ink.
 15. The method ofclaim 14, wherein said forming of the layer of conductive materialcomprises forming tantalum aluminum.
 16. The method of claim 14, whereinsaid patterning and etching comprises forming the only resistorstructure that is utilized for nucleating ink.
 17. The method of claim14, wherein said patterning and etching comprises forming the resistorelements to have substantially the same resistances.
 18. A method ofoperating an ink jet printer comprising: providing at least one resistorstructure configured to heat and eject ink towards a print medium, theone resistor structure comprising: a first resistor element; and atleast one other resistor element, the resistor elements being connectedin parallel and having substantially the same resistances, the resistorelements being configured for redundancy such that if one of theresistor elements fails, one or more remaining resistor elements canfunction to effectuate ink ejection, said resistor elements comprisingthe only resistive structure that is utilized for heating and ejectingink; heating an amount of ink using the resistor elements by applying aseries of voltage pulses to the resistor elements, said heating beingsufficient to cause ink to eject towards the print medium.
 19. Themethod of claim 18 further comprising, in the event of at least one ofthe resistor elements failing, continuing said act of heating sufficientto cause ink to eject towards the print medium.
 20. The method of claim18 further comprising sensing a resistance change associated with theone resistor structure and indicative of a resistor element failure, andresponsive thereto, modifying the series of pulses that are applied tothe resistor elements.
 21. The method of claim 18, wherein saidproviding comprises providing resistor elements comprising the samematerial.
 22. The method of claim 18, wherein said providing comprisesproviding resistor elements comprising tantalum aluminum material. 23.The method of claim 18, wherein said providing comprises providing tenresistor elements for each resistor structure.